The present invention relates to a data transmission method, in which an encoded data signal is transmitted in the form of a data stream of data bursts between a transmitter and a receiver, and to a corresponding data transmission apparatus.
Although in principle the present invention can be employed for arbitrary data transmissions, it will be explained along with the problems it seeks to solve with regard to a cellular CDMA (Code Division Multiple Access) data transmission system.
In particular, by means of CDMA, a plurality of data streams can be transmitted simultaneously over a joint frequency band, as known for instance from K. D. Kammeyer, Nachrichtenübertragung [Communications Transmission], 2nd Edition, in the series entitled Informationstechnik, published by Teubner, Stuttgart, 1996.
In CDMA, a simultaneous transmission of multiple data is effected by encoding the data with codes that are as much as possible uncorrelated, and by superposition of the encoded signals.
In data transmission, among other things, data transmitted in succession or simultaneously interfere with one another; that is, troublesome interference typically occurs in the transmission, in particular intersymbol interference (ISI) from multi-path transmission, and multiple access interference (MAI) by correlated codes.
The following methods are known for interference treatment:                a rake receiving device, located in the receiver, for treating the ISI, as known from John G. Proakis: “Digital Communications”, 3rd Edition, McGraw-Hill, New York, etc., 1995;        joint detection (JD) in the receiver for treating ISI and MAI, as known from A. Klein, G. K. Kaleh and P. W. Baier: Zero Forcing and Minimum Mean-Square-Error Equalization for Multiuser Detection in Code-Division Multiple Access Channels, IEEE Trans. Vehic. Tech., Vol. 45 (1996), 276-287;        pre-rake combining in the transmitter for treating ISI, as known from R. Esmailzadeh and M. Nakagawa: “Pre-Rake Diversity Combination for Direct Sequence Spread Spectrum Mobile Communications Systems”, IEICE Trans. Comm., Vol. E76-B (1993), 1008-1015; and        a joint preequalization in the transmitter for treating ISI and MAI.        
In this type of data transmission, preequalization in the transmitter is an important interference treatment. Joint preequalization in the transmitter of data signals to be transmitted makes simple data detectors possible. In transmission channels that change quickly, however, preequalization in the transmitter leads to higher error rates than with interference treatment techniques in the receiver. For preequalization, the transmitter must know the pulse response of the transmission channel to be used. The TDD (Time Division Duplex) method makes it possible to achieve this knowledge. Accordingly, the channel is estimated before the data transmission.
The following have proved to be disadvantages of the prior art:                the rake receiving device does not eliminate MAI;        JD is very complicated;        joint preequalization is usable only for channels that change slowly.        